Many patients that suffer what is commonly called a heart attack have a myocardial infarction. Myocardial infarction is a necrosis of cardiac tissue brought on by a reduction in blood flow to the infarcted area caused by either a chronic obstruction in an artery or an acute obstruction such as a thrombus in the artery. Hence, myocardial infarction is a total blockage of a cardiac artery.
Ischemia (I) of a heart also results in decreased blood flow, but not as pronounced. It is caused by a partial blockage of an artery and, in many cases, leads to a myocardial infarction.
Both ischemia and myocardial infarction are conditions which are desirably found at an early stage. This is true especially for a myocardial infarction as a heart attack could be eminent. Unfortunately, many people fail to seek prompt treatment for myocardial infarction (MI) until it is too late because most causes of chest pain are not cardiac related.
To monitor patients for ischemia and myocardial infarction, physicians may rely upon periodic EKGs (electrocardiograms) which generally require as many as ten leads to be attached to the patient. In addition, after the EKG, physicians then generally require the patient to take a stress test wherein the patient is caused to run on a treadmill until the patient is essentially exhausted to stress the heart. During and after the treadmill exercise the twelve lead EKG is used to determine if the heart continues to receive adequate blood supply while under the stress conditions. Obviously such monitoring is inconvenient to the patient. Physicians may also rely upon Holtor monitoring recordings which may last from 24 to 48 hours. These additional monitoring techniques are equally as inconvenient and in addition, are also annoying. Since all of these monitoring techniques can, at best, only be administered periodically as a practical matter, and because episodes of myocardial infarction are unpredictable events, all too often, a myocardial infarction is not detected until the patient has already experienced heart damage.
From the foregoing, it can be seen that for some patients, it is very desirable to monitor for ischemia and myocardial infarction. Many of these patients will already have an implanted cardiac stimulation device such as a pacemaker or a combined pacemaker and defibrillator.
Implantable cardiac devices have been proposed in the art for detecting and monitoring ischemia. Many of these devices may be solely for monitoring or incorporated into pacemakers and defibrillators. With modern day storage technology and telemetry, these devices are capable of collecting and communicating large amounts of ischemia data. Unfortunately, these prior devices are incapable of distinguishing between ischemia and the more serious condition of myocardial infarction.